Sorry to be pendactic here, but I don't believe your friend was "abused through Craigslist." Instead, he was abused by the lowlife thieves that stole his property. Actually I think it would be correct to say that he was abused through craigslist, by the person who made the fraudulent post, by AND through the lowlife thieves. "Through" indicates how or where it happened; "by" indicates who did it. ("I was threatened through the mail by a crazed stalker.") In this case the people who took the stuff were both how the abuse took place, since the person who posted the ad used them to accomplish the victimization, and who performed the physical taking of property. Of course the ad-poster would be the other who, without whom the taking wouldn't have happened. Craigslist is where and the other how. Which makes it mostly a social problem, but not entirely.
All of this brings up an interesting question... am I guilty of being ironically pedantic if I point out that "pendactic" isn't a word?
All of this brings up an interesting question... am I guilty of being ironically pedantic if I point out that "pendactic" isn't a word?